JS Built-ins
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Closuresintermediate

Closures — Nested closures

📖 Usage Example
const outer = (a) => (b) => (c) => a + b + c
const step1 = outer(10)
const step2 = step1(5)
step2(3)  // → 18

Each nesting level creates a new closure that accumulates captured variables from all outer scopes, enabling composable step-by-step function application.

Multiple Levels of Nesting

A function can close over variables from multiple outer scopes, creating nested closures.

Challenge: Create a function that returns a function, which in turn returns another function. Each level should capture and use variables from its outer scope.

Example:

const outer = (a) => {
  return (b) => {
    return (c) => a + b + c
  }
}
outer(1)(2)(3)  // 6
💡 Hints (3)
  • • Each function returns another function
  • • Inner functions have access to all outer scopes
  • • This pattern enables partial application